This invention relates to a magnetic recording medium which has an excellent reliability and permits magnetic recording at a high density, a process for producing said magnetic recording medium, and a magnetic disc apparatus used as an auxiliary storage for computer.
Magnetic disc apparatus used in storages such as large computers, workstations, personal computers, etc. are growing in importance year by year and have been increased in capacity and reduced in size. For the capacity increase and size reduction of the magnetic disc apparatus, increasing their density is indispensable. An example of technique for realizing the density increase is the reduction of the distance between the magnetic recording layer of a magnetic recording medium and a magnetic head.
Magnetic recording media produced by sputtering have comprised a protective film for protecting a magnetic film against sliding on a magnetic head. The reduction of thickness of the protective film and the reduction of the distance between the protective film surface and the magnetic head are the most effective means for reducing the distance between the magnetic recording layer and the magnetic head. As the protective film, carbon films formed by DC sputtering, RF sputtering (JP-A-5-174369) or CVD (JP-A-4-90125) are most generally used. For obtaining a protective film having a higher strength, a method of incorporating nitrogen atoms, hydrogen atoms, etc. into the film (JP-A-62-246129 and JP-A-5-22556) has been generally adopted.
As a conventional interface method for a magnetic recording medium and a magnetic head, there is contact-start-and-stop (CSS) method in which at the time of non-working, the magnetic head is stationary in contact with the magnetic recording medium at a predetermined position on the medium where very small concavities and convexities have been formed for preventing adhesion between the magnetic recording medium and the magnetic head, and at the time of working, i.e., the time of record writing, record reading or waiting, the magnetic head is lifted while keeping a very narrow space between the magnetic head and the magnetic recording medium.
In the case of magnetic disc apparatus to which this method is applied, the problem of wear and fracture of the protective film of a magnetic recording medium caused by contact or friction between the magnetic recording medium and a magnetic head at the beginning or end of working becomes more serious with a reduction in the thickness of the protective film. Also at the time of working, the problem of wear and fracture of the protective film caused by accidental contact between the magnetic recording medium and the magnetic head becomes more serious with a reduction in the distance between the protective film surface of the magnetic recording medium and the magnetic head.
It has been proposed that the durability of the protective film is improved by making the thickness of the protective film in an area where CSS is carried out (hereinafter referred to as CSS area), larger than that in an area where data are written (hereinafter referred to as data area) (JP-B-60-23406). However, no sufficient effect can be obtained by merely changing the film thickness because at present, the increase of the capacity and the reduction of the size are absolutely necessary. In detail, the above-mentioned data area has to be as wide as possible in order to record data as much as possible in the limited area of a disc. Therefore, the CSS area and the data area are unavoidably adjacent to each other. In such a condition, it is industrially difficult to make the film thickness in the CSS area widely different from that in the data area. Even if such a thickness change is realized, the reference position of the disc surface is abruptly changed when a head is allowed to seek between the CSS area and the data area. Thus, the thickness change causes an attitude change.
Therefore, the possible thickness difference is at most about 5 nm, and merely changing the thickness of a single film has been hardly effective. In addition, a thinned portion of about 10 nm thick of the protective film in the data area has to have a certain degree of hardness because it is easily fractured by its accidental collision with a magnetic head. However, when the protective film has such a hardness, it is too hard in the CSS area and hence has a high contact resistance with the head, resulting in a deteriorated durability.
From such a point of view, it seems effective to make physical properties of the protective film in the CSS area different from those in the data area. It has been proposed to form a protective film composed mainly of diamond in the CSS area and composed mainly of a mixture of graphite and diamond in the data area (JP-A-3-272017). However, when such a protective film is thinned to about 10 nm, it is not sufficient in strength in the CSS area and hence is easily fractured by contact or friction between a magnetic recording medium and a magnetic head at the beginning or end of working.
Further, it has been proposed to form a graphite structure in the CSS area and an amorphous structure in the data area (JP-A-4-32021). However, it is clear that a thin film with a graphite structure having a thickness of about 10 nm cannot withstand CSS. Even by combining the technique of JP-B-60-23406 with the techniques of JP-A-3-272017 and JP-A-4-32021, there could not be obtained a magnetic recording medium which had a sufficient strength to withstand its accidental collision with a magnetic head and was free from wear and fracture of its protective film in the CSS area by contact or friction between the magnetic recording medium and the magnetic head at the beginning or end of working even if the thickness of the protective film in the data area was adjusted to about 10 nm or less.
In addition, when a protective film composed of a portion having properties suitable for the CSS area and a portion having properties suitable for the data area is formed by a sputtering method, or when the thickness of a protective film is increased only in the CSS area by a sputtering method, even the formation of the protective film in the data area by the use of, for example, a masking shield out of contact with a magnetic recording medium can limit, only to a certain extent, sputtering particles which pass around behind the masking shield and intrude the data area, because of properties of sputtering. Thus, it has been difficult to make film properties in the CSS area strikingly different from those in the data area or change the film thickness markedly in a short distance.
Ion beam deposition is known as a means for forming a protective filmy layer which is tough even at a film thickness smaller than that of a protective filmy layer composed mainly of carbon by sputtering. However, it is industrially difficult to form a protective filmy layer only by ion beam deposition because the life of a hot filament used in an ion gun is short.
The present invention was made in view of such problems. A first object of the present invention is to provide a magnetic recording medium which has a sufficient impact resistance to withstand its accidental collision with a magnetic head and is free from wear and fracture of its protective film in the CSS area by contact or friction between the magnetic recording medium and the magnetic head at the beginning or end of working even if the thickness of the protective film in the data area is reduced to about 10 nm or less.
A second object of the present invention is to provide a process for producing a magnetic recording medium capable of achieving the first object. A third object of the present invention is to provide a magnetic storage suitable for attaining both a high packing density and a high reliability by using a magnetic recording medium obtained by achieving the above first object.
A fourth object of the present invention is to provide a process for producing a magnetic recording medium comprising a substrate, a magnetic film formed thereon and a protective film formed thereon for the protection of said magnetic film and composed mainly of carbon, said magnetic recording medium having sufficient impact resistance and lifting stability in the data area and a sufficient reliability on resistance to sliding in the CSS area, which process uses both an ion beam deposition method and a sputtering method.
A fifth object of the present invention is to provide a magnetic recording medium obtained as a result of achieving the fourth object. A sixth object of the present invention is to provide a magnetic storage suitable for attaining both a high packing density and a high reliability by using a magnetic recording medium obtained by achieving the above fifth object.
For solving the problems described above, the present invention employs the following constitutions:
A magnetic recording medium comprising a substrate, a magnetic film formed thereon and a protective film formed thereon for the protection of said magnetic film and composed mainly of carbon, wherein
a portion of said protective film where said protective film comes into contact with a magnetic head at the time of starting and/or standing of said magnetic head is composed mainly of carbon and nitrogen, and
the portion other than said contact portion of said protective film is composed mainly of not only carbon and nitrogen but also hydrogen for increasing the hardness of the protective film;
A magnetic recording medium comprising a substrate, a magnetic film formed thereon and a protective film formed thereon for the protection of said magnetic film and composed mainly of carbon, wherein
the hardness of a portion of said protective film where said protective film comes into contact with a magnetic head at the time of starting and/or standing of said magnetic head is less than 19 Gpa and not less than 15 Gpa, and
the hardness of the portion other than said contact portion of said protective film is 19 Gpa or more;
A magnetic recording medium comprising a substrate, a magnetic film formed thereon and a protective film formed thereon for the protection of said magnetic film and composed mainly of carbon, wherein
a portion of said protective film where said protective film comes into contact with a magnetic head at the time of starting and/or standing of said magnetic head is composed mainly of carbon and nitrogen and has a hardness of less than 19 Gpa and not less than 15 Gpa, and
the portion other than said contact portion of said protective film is composed mainly of carbon, nitrogen and hydrogen and has a hardness of 19 Gpa or more;
The above-mentioned magnetic recording medium wherein
the thickness of the portion other than said contact portion of said protective film is 15 nm or less;
A process for producing a magnetic recording medium comprising a substrate, a magnetic film formed thereon and a protective film formed thereon for the protection of said magnetic film and composed mainly of carbon, which comprises
forming a protective filmy layer capable of constituting substantially the whole surface of said magnetic recording medium, by a sputtering method using H2 in addition to either only N2 or a combination of N2 and at least one of Ne, Ar, Kr and Xe, and then
forming another protective filmy layer thereon as a portion of said protective film where the protective film comes into contact with a magnetic head at the time of starting and/or standing of said magnetic head, by a sputtering method using either only N2 or a combination of N2 and at least one of Ne, Ar, Kr and X, after taking a means for preventing the adhesion of sputtering particles in the portion other than said contact portion;
A process for producing a magnetic recording medium comprising a substrate, a magnetic film formed thereon and a protective film formed thereon for the protection of said magnetic film and composed mainly of carbon, which comprises
forming a filmy layer as a portion of said protective film where said protective film comes into contact with a magnetic head at the time of starting or standing of said magnetic head, by an ion beam method using either only a hydrocarbon gas or a combination of a hydrocarbon gas and at least one of Ne, Ar, Kr and Xe, and then
forming another protective filmy layer capable of constituting substantially the whole surface of said magnetic recording medium, by a physical vapor deposition method or a chemical vapor deposition method;
A process for producing a magnetic recording medium comprising a substrate, a magnetic film formed thereon and a protective film formed thereon for the protection of said magnetic film and composed mainly of carbon, which comprises
forming a protective filmy layer capable of constituting substantially the whole surface of said magnetic recording medium, by a physical vapor deposition method or a chemical vapor deposition method, and then
forming another filmy layer thereon as a portion of said protective film where said protective film comes into contact with a magnetic head at the time of starting or standing of said magnetic head, by an ion beam method using either only a hydrocarbon gas or a combination of a hydrocarbon gas and at least one of Ne, Ar, Kr and Xe; and
A magnetic recording medium comprising a substrate, a magnetic film formed thereon and a protective film formed thereon for the protection of said magnetic film and composed mainly of carbon, wherein
a portion of said protective film where said protective film comes into contact with a magnetic head at the time of starting or standing of said magnetic head comprises a diamond-like (DLC) layer composed mainly of carbon and hydrogen and an amorphous carbon layer composed mainly of carbon, a combination of carbon and nitrogen, or a combination of carbon, nitrogen and hydrogen, and
the portion other than said contact portion of said protective film comprises an amorphous carbon layer composed mainly of carbon, a combination of carbon and nitrogen, or a combination of carbon, nitrogen and hydrogen.